Two-cylinder, four-stroke-cycle, double-piston engine, especially air-flow-cooled for motorcycles

ABSTRACT

An especially air-flow-cooled two-cylinder, four-stroke-cycle, double-piston engine (1) for the preferred use in motorcycles has for each cylinder (32) a camshaft (14) disposed horizontally on top in the cylinder heads (33) for the drive of valves (37 and 38) disposed in vertical V-positions. An intermediate shaft (4) is connected in the drive of the camshafts (14) which is driven by the crankshaft (3) with 1:2 down-gearing, with said intermediate shaft (4) being arranged parallel below the crank shaft (3), being driven at its front end--in driving direction--, carrying a pump wheel (12&#39;) of a lubricating-oil pump (12) and having two 1:1 drives (13) leading from its rear end in one tunnel each (36) of the cylinders (32) and cylinder heads (33) to the camshafts (14). The camshafts (14) are arranged in the V-space of the valves (37 and 38) and are in driving connection with the valves (37 and 38) by means of rocking levers (39). The intake connections (28&#39;) and the exhaust pipes (53) lead out of the cylinder heads (33) approximately vertically upward and downward.

The invention concerns a two-cylinder, four-stroke-cycle, double-pistonengine of a construction for example, of the air-flow-cooled type formotorcycles, having a camshaft for each cylinder, with said camshaftbeing disposed on top and horizontally disposed, parallel to thecrankshaft and 1:2-geared-down with respect to said crank shaft, withthe camshaft being driven by an intermediate shaft geard downapproximately 1:2 with respect to the speed of the crank shaft andarranged parallel to the crank shaft, by means of, in each case, oneapproximately 1:1 transmitted chain or belt drive, in which case, thechain or belt drives are disposed in driving direction behind thecylinders.

A known double-piston engine of this construction according to DE-OS No.27 03 520 has a relatively fissured outer shape resulting especiallyfrom the arrangement of the valves and their gear. The reason is thatthe intermediate shaft for the drive of the two upper camshafts isarranged above the crankshaft, and the chain or belt drives extend, withseparate coverings which are arranged at a distance from the cylindersand the cylinder heads, to control housings which, in each case, projectfrom the cylinder head. The arrangement of, in each case, parallel inletand outlet valves also contributes to the unsymmetrical and fissuredconstruction of this double-piston engine. In addition, the housingcomponents which project considerably beyond the basic contour of thecylinders and cylinder heads also result in a high cost of constructionand correspondingly heavy weight.

It is the objective of the invention to avoid the above-mentioneddisadvantages and to create a double-piston engine on the basis of theknown construction which has a compact overall structure with low costof construction and low weight, favorable conditions for good groundclearance when installed into motorcycles, an efficient and speed-fixedcontrol with a V-valve arrangement, a largely smooth and appealing outershape that is easy to clean as well as finally a good cooling-air flowat the cylinders and cylinder heads when it is air-flow-cooled.

In order to achieve this manifold objective, the invention provides anarrangement of the intermediate shaft below the crank shaft the drive ofthe intermediate shaft being at the front end of the crank shaft with apump wheel of a lubricating-oil pump on the intermediate shaft. Thechain or belt drives are in tunnels of the cylinders and cylinder heads,the valves with the drive by means of rocking levers in verticalV-position with the camshaft in the V-space, and the intake andexhaust-gas lines to and from the cylinder heads extending essentiallyvertically upward and downward. By means of these characteristics, theobjective of the invention is achieved in a surprisingly favorablemanner. Because of these characteristics, the valve drive including theoil-pump drive, requires very little space, without housing parts orcoverings projecting beyond the basic contour of the engine components.The valve, camshaft and gas-changing duct arrangements also result in avery compact overall structure of the double-piston engine, with theintake and exhaust-gas systems resting closely against the outsidecontours on the upper side and the bottom side of the cylinders andcylinder heads.

The V-positions of the valves are, in each case, in their verticalplane, and are swivelled upward at an angle with respect to ahorizontal-symmetrical arrangement so that the outlet valves are slopeddownward by an angle of about 0° to 20°, and the inlet valves are slopedupward at an angle of about 30° to 50°--always in the direction of theirshaft ends. The above arrangements are further improved so that theintake systems on the upper side of the cylinders and cylinder heads ofboth sides come still closer and, on the whole, require even less space,while the exhaust gas ducts on the bottom side of the cylinders andcylinder heads are provided with more space for leading the exhaust gaspipes toward the center of the vehicle which benefits the groundclearance in the case of motorcycles.

For each cylinder, two inlet valves are arranged parallel next to oneanother, in each case, on both sides of the vertical plane of the outletvalve in vertical planes of the same distance.

By the use of two inlet valves and one outlet valve as compared to oneinlet valve and one outlet valve each makes it possible to obtain largervalve time cross sections in the case of a relatively small V-angle ofthe valves, which benefits the above-mentioned spatial advantages alsoand in addition increases or expands the performance and the speed rangeof the engine and makes possible a varying part-throttle control of bothinlet ports.

The inlet valves have a relatively large free distance of their valvedisks, and in the space created by this distance, a taphole for a sparkplug is arranged in the vertical plane of the outlet valve, withoutchamfer, to the valve-seat rings of the inlet valves, in which case thevalve disks of the inlet valves, in their closing position, areapproximately tangent or somewhat overlap the horizontal axis of thecontour of the pertaining cylinder, and are almost tangent to thecontour of the mentioned cylinder. This results in a position of thespark plugs in the center of the combustion chamber or the upper side ofthe cylinder heads which is advantageous for the combustion sequence andthe maintenance, without decreasing the above-mentioned advantages.

The bearing shafts of the rocking levers, in each case, have a pivotbearing journal for the rocking lever which is eccentric with respect totheir stationary bearing journals in the cylinder head. In each case, atleast one stationary bearing journal has a clamping device for thefixation of the rotating position of the bearing shaft. Akey-cross-section is in one piece shaped to each bearing shaft at leaston one front side. These features are advantageous for the speedfixation of the valve control because of the very small moved mass ofthe rocker arms as well as the overall width and the ground clearancefor the installation of the engine into the motorcycle because of thelow overall height of the valve control above the valve shaft ends.

With the above-described features, an engine may have cooling air ductsat the cylinder head for air-flow cooling, characterized in that theV-space of the valves is parallel to the camshaft. In each case, onecooling-air duct is disposed, having an inflow-opening that is open indriving direction and leading, at the opposite end in front of thetunnel of the chain or belt drive into a discharge compartment extendingvertically upward and/or downward. These characteristics areadvantageous in regard to the air-flow cooling of the cylinder headwithout negatively affecting the other advantages of the invention.

The crank chamber is divided in the vertical center plane and thecrankshaft and the intermediate shaft are arranged in the center plane.One main bearing each is arranged on each side of lifting cranks of thecrankshaft that are directly adjacent to one another and one balancingmass each is in one piece shaped onto the crankshaft directly outsidethe two main bearings and inside shaft sealings that are adjacent onboth sides. These characteristics result in a very small distancebetween bearings of the crankshaft bearings and thus low bending momentsfrom the crank forces and thus correspondingly small bendings of thecrankshaft. On the other hand, the lever arm of the balancing masses isrelatively large, by means of which these can be kept small and theoverall weight of the engine is decreased correspondingly.

The balancing masses are developed as narrow disks and are arranged incorrespondingly narrow annuli of the crank chamber between the mainbearings and the shaft sealings. These characteristics therefore containa corresponding weight- and space-saving development and arrangement ofthe balancing masses.

A double-piston engine configured as above described may have asurrounding fastening flange shaped onto the crank chamber at its topside, with the fastening flange having a number of fastening openingsand/or tapholes for the fastening or the fastening screws of ahollow-plate frame piece. Within the top side enclosed by the fasteningflange, a crank chamber ventilating opening leads out. Such aconfiguration results in a connection that is easy to seal, with adistributed introduction of forces, from a hollow-plate carrier of theframe into the crankchamber, in which case lines for the crank chamberventilation are not necessary when the hollow-plate carrier of the frameis used as the intake space for the combustion air of the engine.

A double-piston engine as described above may have an essentiallysmooth-surfaced front wall lid of the crank chamber covering thesecondary aggregates (generator) and/or the drive of the intermediateshaft, characterized in that an opening for the mounting of an oilfilter installed in longitudinal horizontal position in the crankchamber is arranged in the wall of the crank housing that is covered bythe front wall lid, with the opening having a detachable lid withone-piece connecting ducts to the oil ducts in the crank chamber. Thesefeatures result in an arrangement of the closing lid for an oil filteravoiding a conventional fissured part of the outside wall with dirttraps. The accessibility for the oil filter exchange is maintained in anunchanged manner because during servicing work, the front wall lid mustbe taken off anyhow in order to examine other secondary aggregates.

Since the characteristics described above as the development of acylinder head irrespective of a certain arrangement of the cylinders,have independent inventive significance, they may take the form of acylinder head for four-stroke-cycle internal-combustion engines, havinginlet and outlet valves suspended in V-position in the cylinder head, inwhich case, for each cylinder, two inlet valves are arranged parallelnext to one another corresponding to a V-leg and an outlet valve isarranged corresponding to a second V-leg, the outlet valve beingarranged in a parallel plane of equal distance containing the cylinderaxis, between the two inlet valves, wherein the V-position of the inletand outlet valves in regard to the cylinder axis is swivelled around atsuch an angle with respect to a symmetrical arrangement to the cylinderaxis to the side of the inlet valves, that the outlet valve encloses anangle of about 0° to 20° and the plane determined by the inlet valvesencloses an angle of about 30° to 50° with the cylinder axis, and theinlet valves have a relatively large free distance of their valve disksin which case in the area within this distance, as well as in thevertical plane determined by the outlet valve and the cylinder axis, aspark plug is arranged. The valve disks of the inlet valves in theirclosing position overlap that axis (horizontal axis) of the cylinderthat is located in parallel to the plane determined by the inlet valves.

A double-piston engine and/or a cylinder head as described above,characterized in that the longitudinal axis of the spark plug with thecylinder axis encloses a larger angle--about 45° to 75°--than the planedetermined by the inlet valves.

The invention results in a space requirement of the spark plug thatavoids an excessive distance of the inlet valves and their valvesprings. It may be used advantageously in the case of the double-pistonengine as described above as well as in the case of the cylinder head ofthe character described above.

These and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in connection with the accompanying drawings which show, for thepurposes of illustration only, one embodiment in accordance with thepresent invention, and wherein:

FIG. 1 shows a longitudinal section of an air-flow-cooled, two-cylinder,four-stroke-cycle, double-piston engine for motorcycles havinghollow-plate frame pieces flanged to the upper side of the crankchamber, in a diagrammatic representation.

FIG. 2 shows a partially cut front view according to the Arrow II inFIG. 1;

FIG. 3 is a partially cut plan view according to the Line III--III inFIG. 2;

FIG. 4 is an inside view of the combustion chamber in the cylinder headwith the valve and spark-plug arrangement according to the Line IV--IVin FIG. 3;

FIG. 5 is a top view of the open valve control according to Line V--V inFIG. 3; and

FIG. 6 shows a longitudinal section through the cooling-air duct in thecylinder head according to the Line VI--VI in FIG. 3.

An air-flow-cooled two-cylinder, four-stroke-cycle, double-piston engine1 has a crank chamber 2 that is divided in its vertical centrallongitudinal plane I--I. In FIG. 1, therefore, the longitudinal sectionin the area of the crank chamber is formed by leaving off its one half.In the central longitudinal plane I--I, a one-piece crankshaft 3 as wellas an intermediate shaft 4 are disposed in sleeve bearings. At itsdriven end, the crankshaft 3 carries a flywheel 5, and at its oppositefront end, a generator 6 as well as a toothed-belt wheel 7 for the 1:2geared-down driving connection by means of a toothed belt 8 and anothertoothed-belt wheel 9 to the intermediate shaft 4. On both sides of itslifting cranks 3' and outside its main bearings 10, one each relativelynarrow disk-shaped balancing mass 11 is shaped onto the the crankshaft3, with said balancing masses 11 being arranged in correspondinglynarrow annuli 2' of the crank chamber 2 between the main bearings 10 andthe connecting shaft packings 10'. By means of the relatively largedistance of the balancing masses 11, their balancing function isincreased and their weight is reduced. By means of their arrangement,the distance of the main bearings 10 and thus the weight of the crankchamber 2 is reduced.

The intermediate shaft 4 drives a lubricating-oil pump 12, of which apump wheel 12' is fastened on the intermediate shaft 4, as well as twochain drives 13 each to an upper camshaft 14. In the crank chamber 2, anoil filter 15 is also disposed, the filter unit 16 of which isaccessible for maintenance work by means of an inside lid 17. The lid17, the toothed-belt drive 7, 8 and 9, and the generator 6 are protectedfrom environmental influences by a largely smooth-surfaced front-walllid 18, with said lid, at the same time, facilitating the cleaning ofthe front side of the crank chamber 2.

On the rear side of the crank chamber 2, the flywheel 5 is framed by amounting flange 19 for the connection of a gear housing that is notshown. Shaped to the upper side of the crank chamber 2 is a surroundingmounting flange 20 having a number of mounting holes 21 for mountingscrews 22, to which a hollow-plate frame piece 23 is screwed. Within theupper side of the crank chamber 2 that is surrounded by the mountingflange 20, a crank chamber ventilation opening 24 leads out. Thehollow-plate frame piece 23 connects the crank chamber 2, on a widebending-resistant basis, with a control head 25 of a motorcycle. On itsfront side, the hollow-plate frame piece 23 has an intake air filter 26,through which filtered intake air through openings 27 flows into theinside of the hollow-plate frame piece 23. This is used as the intakespace for the combustion air of the engine and contains length-adjustedintake pipes 28 which lead the combustion air to one carburetor 29 each.The carburetors 29 are partially located within indentations 30 of thehollow-plate frame part 23 having sealed openings 31 for the passage ofthe intake pipes 28, within said recesses 30.

Flanged to both sides of the crank chamber 2 is one cylinder 32 each,and flanged to said cylinder 32 is one cylinder head 33 each having onecylinder-head lid 34 each. The cylinder 32, the cylinder head 33 and thecylinder-head lid 34 have numerous cooling ribs 35 for air-flow cooling.They also each have a tunnel 36 for receiving the chain drives 13, whichextend from the intermediate shaft 4 in the crank chamber 2 to thecamshafts 14 in the cylinder heads 33, in driving direction, on the rearside of the cylinders 32 and the cylinder heads 33. The chain drives 13have a 1:1 transmission, so that on the intermediate shaft 4 as well ason the camshafts 14, small chain wheels 13' may be used. These requirelittle space, even in the cylinder heads 33 and the cylinder-head lids34. The valve control for in each case two inlet valves 37 and oneoutlet valve 38 by means of three rocker arms 39 as transmissionelements from the camshaft 14 to the valves 37 and 38, on the otherhand, has a somewhat larger lateral range so that the cylinder-head lids34 have an outside shape that is rounded off to all sides and has noprojections. This improves their outside appearance and facilitatestheir cleaning and results in a smaller overall width of thedouble-piston engine and also of the motorcycle (FIGS. 2 and 3) equippedwith said engine.

The valves 37 and 38 are arranged in vertical V-position. The two inletvalves 37 are, in each case, arranged in parallel to one anothercorresponding to a V-leg determined by the plane of the two inlet valves37 and having an upward slope of about 37°--seen in the direction towardthe shaft end of the inlet valves 37. The V-leg determined by the outletvalves 38, on the other hand, has a corresponding downward slope ofabout 15°. The camshafts are each disposed in a position that cuts theangle in half within the approximate 52°-V-position of the valves 37 and38.

The rocker arms 39 for the drive of in each case one valve 37 and 38 arerotatably disposed on bearing shafts 40. Their pivot-bearing journals 41are disposed eccentrically with respect to their stationary-bearingjournals 42 for the valve-clearance adjustment (FIGS. 2 and 5). Theirstationary-bearing journals 42 can be fastened in bearing blocks 44 ofthe cylinder head 33 so that they are firm with respect to rotation,with said bearing blocks 44 being able to be locked in place by means ofscrews 43. For the valve-clearance adjusting process, a key profile--notshown in the drawing--is shaped onto the bearing shafts 40 at, in eachcase, one accessible front end. In this case, an inside profile ispreferred because it requires no space and reduces weight as a recess inthe material. The valve control as a whole therefore requires littlespace and cost of construction and contains no additional movedcomponents for the valve-clearance adjustment.

An advantageous development of the combustion chamber 46 (FIGS. 2 and 4)is obtained on the basis of the above-described V-position of the valves37 and 38 in connection with the arrangement of, in each case, the twoinlet valves 37 and their valve disks 37' at a relatively large freedistance, and the arrangement of a spark plug 45 in the space created bythis distance. The valve disks 37' and 38' of the inlet 37 and outletvalves 38 rest almost tangently close on the pertaining contour 32' ofthe pertaining cylinder 32 as well as at a relatively narrow distancebetween the valve disk 37' and in each case one valve disk 38'. In thiscase, the valve plates 38' overlap the horizontal axis 32" of thecontour 32'. The spark gap of the spark plug 45 is located centrallybetween the valves 37 and 38 in the combustion chamber 46. In the upperarea of the combustion chamber 46, a large press area 47 can bedeveloped which interacting with a flat bottom section of a piston 48permits a press gap with a favorable influence on the combustionprocess. The spark plug 45 is arranged in a steeper slope than the inletvalves 37 in the vertical plane 49 together with the outlet valve 38.The space requirement for the installation of the spark plug istherefore not set off (sic) between the space requirement of the valvesprings 50 of the inlet valves 37. In addition, the spark plugs andtheir electrical connections therefore have an especially favorableaccessibility for servicing purposes.

For the air-flow cooling of the cylinder heads 33, a cooling-air duct 51that is open and horizontal in driving direction is provided parallel tothe camshaft 14 in the V-space of the valves 37 and 38. Said cooling-airduct 51, at its end that is opposite to the driving direction, leadsinto a vertical discharge duct 52 which is disposed in front of thetunnel 36 of the chain drive 13 and is open toward the top and thebottom. This ensures a highly effective cooling of the cylinder heads 33without additional requirements in regard to space and cost.

A favorable space-saving arrangement results from the above-describedarrangement of valves also for the exhaust connections 28' with thecarburetors 29 and for the exhaust gas pipes 53. While the intake systemat the top side of the engine, in a space-saving manner, rests closelyagainst the hollow-plate frame part 23 and therefore has a narrow width,sufficient space is available for the exhaust-gas lines 53 withrelatively large radii with little resistance in regard to flow, withoutimpairing the ground clearance and sloping-position clearance for themotorcycle driving operation.

The overall construction of the two-cylinder, four-stroke-cycle,double-piston engine, according to the invention, results, mainly forthe use in motorcycles, in a summation of mutually complementingadvantages in regard to high performance, efficient cooling, gooddriving features, low weight and cost of construction, small spacerequirements and an appealing outer shape. However, a large number ofthese advantages also exist in the case of a stationary and/or encloseduse with blast air or liquid cooling.

While I have shown and described only one embodiment in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible to numerous changes and modifications asknown to one having ordinary skill in the art, and I therefore do notwish to be limited to the details shown and described herein, but intendto cover all such modifications as are encompassed by the scope of theappended claims.

I claim:
 1. A cylinder head for four-stroke-cycle internal-combustionengines, having inlet and outlet valves supsended in V-position in thecylinder head, in which case, for each cylinder, two inlet valves arearranged parallel to one another, their shafts corresponding to oneV-leg, and one outlet valve is arranged approximately therebetween theshaft of which corresponds to a second V-leg and substantiallyequidistant from the inlet valves and in a plane containing the cylinderaxis, characterized in thatthe V-position of the inlet and outlet valveshafts is disposed such that the outlet valve shaft enclose an angle ofabout 0° to 20° with the cylinder axis, the plane determined by theinlet valve shafts enclosing an angle of about 30° to 50° with thecylinder axis, an area lying substantially between the inlet valveswhich encompasses the plane determined by the outlet valve shaft and thecylinder axis, a spark plug arranged within said area, and the valvedisks of the inlet valves in their closing position overlap a plane ofthe cylinder cross-section containing the axis of the cylinder and thatis located substantially equidistant from the centers of the valve disksof the inlet valves.
 2. A cylinder head according to claim 1, whereinthelongitudinal axis of the sparkplug with the cylinder axis encloses anangle of substantially 45° to 75°, larger than the angle determined bythe valves.
 3. A cylinder head in accordance with claim 1, wherein theouter periphery of the inlet and outlet valves lie entirely within theperiphery of the cylinder.